U.S. Pat. No. 4,687,042 states that a shell of a semi-solid slug can be prevented from entering a die cavity by placing the slug in a prechamber of a vertical forging machine and causing a portion of the slug to pass through a coaxial reduced diameter gate, thereby retaining the shell in the prechamber. However, where the shell has been globularized by heating the semi-solid slug, peripheral, globularized portions of the slug are not necessarily prevented from entering the die cavity, and undesired portions of the slug such as surface oxides and other surface impurities of the heated slug can be swept into the die cavity. The present invention is therefore directed to addressing flow control of metal, such as liquid or semi-solid metal, into a part forming die.
Although plungers of die casting machines generally have substantially planar tips which fill uniform diameter shot chambers, plungers with modified tip arrangements or modified shot sleeves are disclosed in U.S. Pat. Nos. 2,932,865 and 3,528,478, Japanese Patent Publication No. 56-5621, French Patent No. 640,842 and German Patent No. 921,881. U.S. Pat. No. 4,144,734 discloses an extrusion plunger having an annular step for collecting impurities. German Patent Application No. DE-19507995-A1 discloses a die casting arrangement wherein a radially enlarged space is provided at the end of the shot sleeve to trap undesirable material. Despite the existence of these known modifications to plungers and shot sleeves, it would be desirable to optimize flow control and retention of undesired surface portions of metal placed into a shot sleeve during a die filling process using, for example, liquid metal or semi-solid metal which has been heated to globularize any dendritic shell.